That's a simple question, but it has a complicated answer. Basically, "it depends" - on where you live, and which country the book you're talking about was originally published in.

There is an aspect of copyright law called "the rule of the shorter term", which says that if a work is in the public domain in the country that it was originally published in, it will be in the public domain elsewhere, too. The copyright law of some countries (Australia, for example) includes the rule of the shorter term, while that of other countries does not.

EU copyright law does include the rule of the shorter term, but it can be overridden by bilateral copyright treaties between specific countries. There is, for example, such a treaty between the USA and Germany; this means that US published works use a strict "life+70" copyright term in Germany, so works which are in the public domain in the US are not necessarily so in Germany. In the UK it's even more complicated: the rule of the shorter term has and has not applied in UK law at different times, and hence a work that's in the public domain in another country may or may not be in the UK public domain, depending on when it entered the PD in its source country, and whether or not the UK was following the rule of the shorter term at that particular time.

So the answer is that you need to look at the circumstances on a case-by-case basis; there is no general rule that can be applied.